Efficacy of mineral supplementation to growing cattle grazing winter-wheat pasture in northwestern Oklahoma.

Two experiments were conducted to evaluate the efficacy of mineral supplementation to cattle grazing winter-wheat pasture. In experiment 1 (fall), 120 steers and heifers (body weight [BW] = 232 ± 11.4 kg) were assigned randomly to four blocks of replicated pastures during the second week of November in 2008 and 2009 and all herds (6 animals/pasture; 4.9 ha/pasture) were allowed to graze for 84 d. In experiment 2 (spring), 216 steers (BW = 248 ± 7.9 kg) were assigned randomly to five blocks of replicated pastures during the second week of February in 2009 and 2010 and all herds (12 or 6 animals/pasture; 4.9 ha/pasture) were allowed to graze for 84 d. Half the pastures in both experiments received a free-choice mineral mixture (Wheat Pasture Pro; Land O'Lakes Purina Feed, LLC; St. Paul, MN; Ca, 16% and P, 4%); mineral feeders were weighed weekly to determine mineral intake. All pastures were planted in early September of each year (67 kg of seed/ha) and fertilized with 50 kg of urea-N/ha. Standing herbage dry matter was determined midway between weigh dates by clipping wheat forage to the ground along 122 cm of drill rows at 10 locations/pasture. Data were analyzed by ANOVA, with treatment as the fixed effect and pasture, animal sex (experiment 1), and block as random effects. In experiment 1, cattle offered minerals had a 43% faster average daily gain (ADG; P = 0.02, 0.73 kg) than cattle not offered minerals (0.51 kg); hence, supplemented cattle weighed 6% more (P = 0.04; 286 kg) after 84 d than nonsupplemented cattle (271 kg). In experiment 2, cattle offered the mineral supplement had a faster ADG (20% increase; P = 0.04; 1.00 kg) than cattle not offered minerals (0.83 kg). Further, supplemented cattle weighed 4% more (P = 0.03; 326 kg) after 84 d than nonsupplemented cattle (312 kg). In both experiments, daily standing herbage dry matter averaged 1,381 kg/animal and never differed (P ≥ 0.47) between treatments. Mineral intakes averaged 135 (experiment 1) and 124 (experiment 2) g/d, resulting in a cost of supplement to kilogram of added BW gain of $0.53 and $0.64, respectively (assuming a mineral cost of $0.88/kg). Overall, supplementing an appropriate mineral mixture to cattle grazing winter-wheat pasture increased ADG in a cost-effective manner.